In biology, a mutation is the permanent alteration of the nucleotide sequence of the genome of an organism, virus, or extrachromosomal DNA or other genetic elements. Mutations result from errors during DNA replication or other types of damage to DNA, which may undergo error-prone repair, or cause an error during other forms of repair, or else may cause an error during replication. Mutations may result from insertion or deletion of segments of DNA due to mobile genetic elements. Mutations may or may not produce discernible changes in the observable characteristics of an organism. Mutations play a part in both normal and abnormal biological processes including: evolution and the development of the immune system, including junctional diversity; the genomes of RNA viruses are based on RNA rather than DNA. The RNA viral genome can be double single stranded. In some of these viruses replication occurs and there are no mechanisms to check the genome for accuracy; this error-prone process results in mutations.
Mutation can result in many different types of change in sequences. Mutations in genes can either have no effect, alter the product of a gene, or prevent the gene from functioning properly or completely. Mutations can occur in nongenic regions. One study on genetic variations between different species of Drosophila suggests that, if a mutation changes a protein produced by a gene, the result is to be harmful, with an estimated 70 percent of amino acid polymorphisms that have damaging effects, the remainder being either neutral or marginally beneficial. Due to the damaging effects that mutations can have on genes, organisms have mechanisms such as DNA repair to prevent or correct mutations by reverting the mutated sequence back to its original state. Mutations can involve the duplication of large sections of DNA through genetic recombination; these duplications are a major source of raw material for evolving new genes, with tens to hundreds of genes duplicated in animal genomes every million years.
Most genes belong to larger gene families of shared ancestry. Novel genes are produced by several methods through the duplication and mutation of an ancestral gene, or by recombining parts of different genes to form new combinations with new functions. Here, protein domains act as modules, each with a particular and independent function, that can be mixed together to produce genes encoding new proteins with novel properties. For example, the human eye uses four genes to make structures that sense light: three for cone cell or color vision and one for rod cell or night vision. Another advantage of duplicating a gene is. Other types of mutation create new genes from noncoding DNA. Changes in chromosome number may involve larger mutations, where segments of the DNA within chromosomes break and rearrange. For example, in the Homininae, two chromosomes fused to produce human chromosome 2. In evolution, the most important role of such chromosomal rearrangements may be to accelerate the divergence of a population into new species by making populations less to interbreed, thereby preserving genetic differences between these populations.
Sequences of DNA that can move about the genome, such as transposons, make up a major fraction of the genetic material of plants and animals, may have been important in the evolution of genomes. For example, more than a million copies of the Alu sequence are present in the human genome, these sequences have now been recruited to perform functions such as regulating gene expression. Another effect of these mobile DNA sequences is that when they move within a genome, they can mutate or delete existing genes and thereby produce genetic diversity. Nonlethal mutations increase the amount of genetic variation; the abundance of some genetic changes within the gene pool can be reduced by natural selection, while other "more favorable" mutations may accumulate and result in adaptive changes. For example, a butterfly may produce offspring with new mutations; the majority of these mutations will have no effect. If this color change is advantageous, the chances of this butterfly's surviving and producing its own offspring are a little better, over time the number of butterflies with this mutation may form a larger percentage of the population.
Neutral mutations are defined as mutations whose effects do not influence the fitness of an individual. These can increase in frequency over time due to genetic drift, it is believed that the overwhelming majority of mutations have no significant effect on an organism's fitness. DNA repair mechanisms are able to mend most changes before they become permanent mutations, many organisms have mechanisms for eliminating otherwise-permanently mutated somatic cells. Beneficial mutations can improve reproductive success. Mutationism is one of several alternatives to evolution by natural selection that have existed both before and after the publication of Charles Darwin's 1859 book, On the Origin of Species. In the theory, mutation was the source of novelty
The BMJ is a weekly peer-reviewed medical journal. It is one of the world's oldest general medical journals. Called the British Medical Journal, the title was shortened to BMJ in 1988, changed to The BMJ in 2014; the journal is published by the global knowledge provider BMJ, a wholly owned subsidiary of the British Medical Association. The editor in chief of The BMJ is Fiona Godlee, appointed in February 2005; the journal began publishing on 3 October 1840 as the Provincial Medical and Surgical Journal and attracted the attention of physicians around the world through its publication of high-impact original research articles and unique case reports. The BMJ's first editors were P. Hennis Green, lecturer on the diseases of children at the Hunterian School of Medicine, its founder and Robert Streeten of Worcester, a member of the PMSA council; the first issue of the British Medical Journal was 16 pages long and contained three simple woodcut illustrations. The longest items were the editors' introductory editorial and a report of the Provincial Medical and Surgical Association's Eastern Branch.
Other pages included a condensed version of Henry Warburton's medical reform bill, book reviews, clinical papers, case notes. There were 2 1⁄2 columns of advertisements. Inclusive of stamp duty it cost 7d, a price which remained until 1844. In their main article and Streeten noted that they had "received as many advertisements for our first number, as the most popular Medical Journal, after seventeen years of existence."In their introductory editorial and statements and Streeten defined "the main objects of promotion of which the Provincial Medical and Surgical Journal is established". Summarised, there were two clear main objectives: the advancement of the profession in the provinces and the dissemination of medical knowledge. Green and Streeten expressed interest in promoting public well-being as well as maintaining'medical practitioners, as a class in that rank of society which, by their intellectual acquirements, by their general moral character, by the importance of the duties entrusted to them, they are justly entitled to hold'.
The BMJ published the first centrally randomised controlled trial. The journal carried the seminal papers on the causal effects of smoking on health and lung cancer and other causes of death in relation to smoking. For a long time, the journal's sole competitor was The Lancet based in the UK, but with increasing globalisation, The BMJ has faced tough competition from other medical journals The New England Journal of Medicine and the Journal of the American Medical Association; the BMJ is an advocate of evidence-based medicine. It publishes research as well as clinical reviews, recent medical advances, editorial perspectives, among others. A special "Christmas Edition" is published annually on the Friday before Christmas; this edition is known for research articles which apply a serious academic approach to investigating less serious medical questions. The results are humorous and reported by the mainstream media; the BMJ has an open peer review system. About half the original articles are rejected after review in-house.
Manuscripts chosen for peer review are first reviewed by external experts, who comment on the importance and suitability for publication, before the final decision on a manuscript is made by the editorial committee. The acceptance rate is less than 7% for original research articles; the BMJ is included in the major indexes PubMed, MEDLINE, EBSCO, the Science Citation Index. The journal has long criticised the misuse of the impact factor to award grants and recruit researchers by academic institutions; the five journals that as of 2008 have cited The BMJ most are The BMJ, Cochrane Database of Systematic Reviews, The Lancet, BMC Public Health, BMC Health Services Research. As of 2008, the five journals that have been cited most by articles published in The BMJ are The BMJ, The Lancet, The New England Journal of Medicine, Journal of the American Medical Association and Cochrane Database of Systematic Reviews. In the 2018 Journal Citation Reports, The BMJ's impact factor was 23.295 in 2017, ranking it fourth among general medical journals.
According to the Web of Science, the following articles have been cited the most often: Cole TJ, Bellizzi MC, Flegal KM, Dietz WH. "Establishing a standard definition for child overweight and obesity worldwide: international survey". BMJ. 320: 1240–3. Doi:10.1136/bmj.320.7244.1240. PMC 27365. PMID 10797032. "Collaborative meta-analysis of randomised trials of antiplatelet therapy for prevention of death, myocardial infarction, stroke in high risk patients". BMJ. 324: 71–86. January 2002. Doi:10.1136/bmj.324.7329.71. PMC 64503. PMID 11786451. Stratton IM, Adler AI, Neil HA, Matthews DR, Manley SE, Cull CA, Hadden D, Turner RC, Holman RR. "Association of glycaemia with macrovascular and microvascular complications of type 2 diabetes: prospective observational study". BMJ. 321: 405–12. Doi:10.1136/bmj.321.7258.405. PMC 27454. PMID 10938048; as of 2014, the most viewed article on The BMJ website is: Schultz WW, van Andel P, Sabelis I, Mooyaart E. "Magnetic resonance imaging of male and female genitals during coitus and female sexual arousal".
BMJ. 319: 1596–600. Doi:10.1136/bmj.319.7225.1596. PMC 28302. PMID 10600954. In 1974, Dr. Elaine Murphy submitted a brief case report under her husband's name John which suggested a condition known as Cello Scrotum, a fictional condition which affected male ce
Nonsteroidal anti-inflammatory drug
Nonsteroidal anti-inflammatory drugs are a drug class that reduce pain, decrease fever, prevent blood clots and, in higher doses, decrease inflammation. Side effects depend on the specific drug, but include an increased risk of gastrointestinal ulcers and bleeds, heart attack and kidney disease; the term nonsteroidal distinguishes these drugs from steroids, which while having a similar eicosanoid-depressing, anti-inflammatory action, have a broad range of other effects. First used in 1960, the term served to distance these medications from steroids, which where stigmatised at the time due to the connotations with anabolic steroid abuse. NSAIDs work by inhibiting the activity of cyclooxygenase enzymes. In cells, these enzymes are involved in the synthesis of key biological mediators, namely prostaglandins which are involved in inflammation, thromboxanes which are involved in blood clotting. There are two types of NSAID available: COX-2 selective. Most NSAIDs are non-selective, inhibit the activity of both COX-1 and COX-2.
These NSAIDs, while reducing inflammation inhibit platelet aggregation and increase the risk of gastrointestinal ulcers/bleeds. COX-2 selective inhibitors have less gastrointestinal side effects, but promote thrombosis and increase the risk of heart attack; as a result, COX-2 selective inhibitors are contraindicated due to the high risk of undiagnosed vascular disease. These differential effects are due to the different roles and tissue localisations of each COX isoenzyme. By inhibiting physiological COX activity, all NSAIDs increase the risk of kidney disease and, through a related mechanism, heart attack; the most prominent NSAIDs are aspirin and naproxen, all available over the counter in most countries. Paracetamol is not considered an NSAID because it has only minor anti-inflammatory activity, it treats pain by blocking COX-2 in the central nervous system, but not much in the rest of the body. NSAIDs are used for the treatment of acute or chronic conditions where pain and inflammation are present.
NSAIDs are used for the symptomatic relief of the following conditions: Aspirin, the only NSAID able to irreversibly inhibit COX-1, is indicated for antithrombosis through inhibition of platelet aggregation. This is useful for the management of arterial thrombosis and prevention of adverse cardiovascular events like heart attacks. Aspirin inhibits platelet aggregation by inhibiting the action of thromboxane A2. In a more specific application, the reduction in prostaglandins is used to close a patent ductus arteriosus in neonates if it has not done so physiologically after 24 hours. NSAIDs are useful in the management of post-operative dental pain following invasive dental procedures such as dental extraction; when not contra-indicated they are favoured over the use of paracetamol alone due to the anti-inflammatory effect they provide. When used in combination with paracetamol the analgesic effect has been proven to be improved. There is weak evidence suggesting that taking pre-operative analgesia can reduce the length of post operative pain associated with placing orthodontic spacers under local anaesthetic.
Combination of NSAIDs with pregabalin as preemptive analgesia has shown promising results for decreasing post operative pain intensity. The effectiveness of NSAID's for treating non-cancer chronic pain and cancer-related pain in children and adolescents is not clear. There have not been sufficient numbers of high-quality randomized controlled trials conducted. NSAIDs may be used with caution by people with the following conditions: Irritable bowel syndrome Persons who are over age 50, who have a family history of GI problems Persons who have had past GI problems from NSAID useNSAIDs should be avoided by people with the following conditions: The widespread use of NSAIDs has meant that the adverse effects of these drugs have become common. Use of NSAIDs increases risk of a range of gastrointestinal problems, kidney disease and adverse cardiovascular events; as used for post-operative pain, there is evidence of increased risk of kidney complications. Their use following gastrointestinal surgery remains controversial, given mixed evidence of increased risk of leakage from any bowel anastomosis created.
An estimated 10–20% of NSAID patients experience dyspepsia. In the 1990s high doses of prescription NSAIDs were associated with serious upper gastrointestinal adverse events, including bleeding. Over the past decade, deaths associated with gastric bleeding have declined. NSAIDs, like all drugs, may interact with other medications. For example, concurrent use of NSAIDs and quinolones may increase the risk of quinolones' adverse central nervous system effects, including seizure. There is an argument over the benefits and risks of NSAIDs for treating chronic musculoskeletal pain; each drug has a benefit-risk profile and balancing the risk of no treatment with the competing potential risks of various therapies is the clinician's responsibility. If a COX-2 inhibitor is taken, a traditional NSAID should not be taken at the same time. In addition, people on daily aspirin therapy must be careful if they use other NSAIDs, as these may inhibit the cardioprotective effects of aspirin. Rofecoxib was shown to produce fewer gastrointestinal adverse drug reactions compared with naproxen.
This study, the VIGOR trial, raised the issue of the cardiovascular safety of the coxibs. A statistically significant increase in the incidence of myocardial infarctions was observed in patients on rofecoxib. Further data, from the APPROVe trial, s
Deoxyribonucleic acid is a molecule composed of two chains that coil around each other to form a double helix carrying the genetic instructions used in the growth, development and reproduction of all known organisms and many viruses. DNA and ribonucleic acid are nucleic acids; the two DNA strands are known as polynucleotides as they are composed of simpler monomeric units called nucleotides. Each nucleotide is composed of one of four nitrogen-containing nucleobases, a sugar called deoxyribose, a phosphate group; the nucleotides are joined to one another in a chain by covalent bonds between the sugar of one nucleotide and the phosphate of the next, resulting in an alternating sugar-phosphate backbone. The nitrogenous bases of the two separate polynucleotide strands are bound together, according to base pairing rules, with hydrogen bonds to make double-stranded DNA; the complementary nitrogenous bases are divided into two groups and purines. In DNA, the pyrimidines are cytosine. Both strands of double-stranded DNA store the same biological information.
This information is replicated as and when the two strands separate. A large part of DNA is non-coding, meaning that these sections do not serve as patterns for protein sequences; the two strands of DNA are thus antiparallel. Attached to each sugar is one of four types of nucleobases, it is the sequence of these four nucleobases along the backbone. RNA strands are created using DNA strands as a template in a process called transcription. Under the genetic code, these RNA strands specify the sequence of amino acids within proteins in a process called translation. Within eukaryotic cells, DNA is organized into long structures called chromosomes. Before typical cell division, these chromosomes are duplicated in the process of DNA replication, providing a complete set of chromosomes for each daughter cell. Eukaryotic organisms store most of their DNA inside the cell nucleus as nuclear DNA, some in the mitochondria as mitochondrial DNA, or in chloroplasts as chloroplast DNA. In contrast, prokaryotes store their DNA only in circular chromosomes.
Within eukaryotic chromosomes, chromatin proteins, such as histones and organize DNA. These compacting structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed. DNA was first isolated by Friedrich Miescher in 1869, its molecular structure was first identified by Francis Crick and James Watson at the Cavendish Laboratory within the University of Cambridge in 1953, whose model-building efforts were guided by X-ray diffraction data acquired by Raymond Gosling, a post-graduate student of Rosalind Franklin. DNA is used by researchers as a molecular tool to explore physical laws and theories, such as the ergodic theorem and the theory of elasticity; the unique material properties of DNA have made it an attractive molecule for material scientists and engineers interested in micro- and nano-fabrication. Among notable advances in this field are DNA origami and DNA-based hybrid materials. DNA is a long polymer made from repeating units called nucleotides.
The structure of DNA is dynamic along its length, being capable of coiling into tight loops and other shapes. In all species it is composed of two helical chains, bound to each other by hydrogen bonds. Both chains are coiled around the same axis, have the same pitch of 34 angstroms; the pair of chains has a radius of 10 angstroms. According to another study, when measured in a different solution, the DNA chain measured 22 to 26 angstroms wide, one nucleotide unit measured 3.3 Å long. Although each individual nucleotide is small, a DNA polymer can be large and contain hundreds of millions, such as in chromosome 1. Chromosome 1 is the largest human chromosome with 220 million base pairs, would be 85 mm long if straightened. DNA does not exist as a single strand, but instead as a pair of strands that are held together; these two long strands coil in the shape of a double helix. The nucleotide contains both a segment of the backbone of a nucleobase. A nucleobase linked to a sugar is called a nucleoside, a base linked to a sugar and to one or more phosphate groups is called a nucleotide.
A biopolymer comprising multiple linked nucleotides is called a polynucleotide. The backbone of the DNA strand is made from alternating sugar residues; the sugar in DNA is 2-deoxyribose, a pentose sugar. The sugars are joined together by phosphate groups that form phosphodiester bonds between the third and fifth carbon atoms of adjacent sugar rings; these are known as the 3′-end, 5′-end carbons, the prime symbol being used to distinguish these carbon atoms from those of the base to which the deoxyribose forms a glycosidic bond. When imagining DNA, each phosphoryl is considered to "belong" to the nucleotide whose 5′ carbon forms a bond therewith. Any DNA strand therefore has one end at which there is a phosphoryl attached to the 5′ carbon of a ribose and another end a
Blood plasma is a yellowish liquid component of blood that holds the blood cells in whole blood in suspension. In other words, it is the liquid part of the blood that carries cells and proteins throughout the body, it makes up about 55% of the body's total blood volume. It is the intravascular fluid part of extracellular fluid, it is water, contains dissolved proteins, clotting factors, hormones, carbon dioxide and oxygen. It plays a vital role in an intravascular osmotic effect that keeps electrolyte concentration balanced and protects the body from infection and other blood disorders. Blood plasma is separated from the blood by spinning a tube of fresh blood containing an anticoagulant in a centrifuge until the blood cells fall to the bottom of the tube; the blood plasma is poured or drawn off. Blood plasma has a density of 1025 kg/m3, or 1.025 g/ml. Blood serum is blood plasma without clotting factors. Plasmapheresis is a medical therapy that involves blood plasma extraction and reintegration.
Fresh frozen plasma is on the WHO Model List of Essential Medicines, the most important medications needed in a basic health system. It is of critical importance in the treatment of many types of trauma which result in blood loss, is therefore kept stocked universally in all medical facilities capable of treating trauma or that pose a risk of patient blood loss such as surgical suite facilities. Blood plasma volume may be expanded by or drained to extravascular fluid when there are changes in Starling forces across capillary walls. For example, when blood pressure drops in circulatory shock, Starling forces drive fluid into the interstitium, causing third spacing. Standing still for a prolonged period will cause an increase in transcapillary hydrostatic pressure; as a result 12% of blood plasma volume will cross into the extravascular compartment. This causes an increase in hematocrit, serum total protein, blood viscosity and, as a result of increased concentration of coagulation factors, it causes orthostatic hypercoagulability.
Plasma was well-known when described by William Harvey in de Mortu Cordis in 1628, but knowledge of it extends as far back as Vesalius.. The discovery of fibrinogen by William Henson in ca 1770 made it easier to study plasma, as ordinarily, upon coming in contact with a foreign surface – something other than vascular endothelium – clotting factors become activated and clotting proceeds trapping RBCs etc in the plasma and preventing separation of plasma from the blood. Adding citrate and other anticoagulants is a recent advance. Note that, upon formation of a clot, the remaining clear fluid is Serum, plasma without the clotting factors; the use of blood plasma as a substitute for whole blood and for transfusion purposes was proposed in March 1918, in the correspondence columns of the British Medical Journal, by Gordon R. Ward. "Dried plasmas" in powder or strips of material format were developed and first used in World War II. Prior to the United States' involvement in the war, liquid plasma and whole blood were used.
The "Blood for Britain" program during the early 1940s was quite successful based on Charles Drew's contribution. A large project began in August 1940 to collect blood in New York City hospitals for the export of plasma to Britain. Drew was appointed medical supervisor of the "Plasma for Britain" project, his notable contribution at this time was to transform the test tube methods of many blood researchers into the first successful mass production techniques. The decision was made to develop a dried plasma package for the armed forces as it would reduce breakage and make the transportation and storage much simpler; the resulting dried. One bottle contained enough distilled water to reconstitute the dried plasma contained within the other bottle. In about three minutes, the plasma could stay fresh for around four hours; the Blood for Britain program operated for five months, with total collections of 15,000 people donating blood, with over 5,500 vials of blood plasma. Following the "Plasma for Britain" invention, Drew was named director of the Red Cross blood bank and assistant director of the National Research Council, in charge of blood collection for the United States Army and Navy.
Drew argued against the armed forces directive that blood/plasma was to be separated by the race of the donor. Drew insisted that there was no racial difference in human blood and that the policy would lead to needless deaths as soldiers and sailors were required to wait for "same race" blood. By the end of the war the American Red Cross had provided enough blood for over six million plasma packages. Most of the surplus plasma was returned to the United States for civilian use. Serum albumin replaced dried plasma for combat use during the Korean War. Plasma as a blood product prepared from blood donations is used in blood transfusions as fresh frozen plasma or plasma Frozen Within 24 Hours After Phlebotomy; when donating whole blood or packed red blood cell transfusions, O- is the most desirable and is considered a "universal donor," since it has neither A nor B antigens and can be safely transfused to most recipients. Type AB+ is the "universal recipient" type for PRBC donations. However, for plasma the situation is somewhat reverse
Proteins are large biomolecules, or macromolecules, consisting of one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, responding to stimuli, providing structure to cells and organisms, transporting molecules from one location to another. Proteins differ from one another in their sequence of amino acids, dictated by the nucleotide sequence of their genes, which results in protein folding into a specific three-dimensional structure that determines its activity. A linear chain of amino acid residues is called a polypeptide. A protein contains at least one long polypeptide. Short polypeptides, containing less than 20–30 residues, are considered to be proteins and are called peptides, or sometimes oligopeptides; the individual amino acid residues are bonded together by peptide bonds and adjacent amino acid residues. The sequence of amino acid residues in a protein is defined by the sequence of a gene, encoded in the genetic code.
In general, the genetic code specifies 20 standard amino acids. Shortly after or during synthesis, the residues in a protein are chemically modified by post-translational modification, which alters the physical and chemical properties, stability and the function of the proteins. Sometimes proteins have non-peptide groups attached, which can be called prosthetic groups or cofactors. Proteins can work together to achieve a particular function, they associate to form stable protein complexes. Once formed, proteins only exist for a certain period and are degraded and recycled by the cell's machinery through the process of protein turnover. A protein's lifespan covers a wide range, they can exist for years with an average lifespan of 1 -- 2 days in mammalian cells. Abnormal or misfolded proteins are degraded more either due to being targeted for destruction or due to being unstable. Like other biological macromolecules such as polysaccharides and nucleic acids, proteins are essential parts of organisms and participate in every process within cells.
Many proteins are enzymes that are vital to metabolism. Proteins have structural or mechanical functions, such as actin and myosin in muscle and the proteins in the cytoskeleton, which form a system of scaffolding that maintains cell shape. Other proteins are important in cell signaling, immune responses, cell adhesion, the cell cycle. In animals, proteins are needed in the diet to provide the essential amino acids that cannot be synthesized. Digestion breaks the proteins down for use in the metabolism. Proteins may be purified from other cellular components using a variety of techniques such as ultracentrifugation, precipitation and chromatography. Methods used to study protein structure and function include immunohistochemistry, site-directed mutagenesis, X-ray crystallography, nuclear magnetic resonance and mass spectrometry. Most proteins consist of linear polymers built from series of up to 20 different L-α- amino acids. All proteinogenic amino acids possess common structural features, including an α-carbon to which an amino group, a carboxyl group, a variable side chain are bonded.
Only proline differs from this basic structure as it contains an unusual ring to the N-end amine group, which forces the CO–NH amide moiety into a fixed conformation. The side chains of the standard amino acids, detailed in the list of standard amino acids, have a great variety of chemical structures and properties; the amino acids in a polypeptide chain are linked by peptide bonds. Once linked in the protein chain, an individual amino acid is called a residue, the linked series of carbon and oxygen atoms are known as the main chain or protein backbone; the peptide bond has two resonance forms that contribute some double-bond character and inhibit rotation around its axis, so that the alpha carbons are coplanar. The other two dihedral angles in the peptide bond determine the local shape assumed by the protein backbone; the end with a free amino group is known as the N-terminus or amino terminus, whereas the end of the protein with a free carboxyl group is known as the C-terminus or carboxy terminus.
The words protein and peptide are a little ambiguous and can overlap in meaning. Protein is used to refer to the complete biological molecule in a stable conformation, whereas peptide is reserved for a short amino acid oligomers lacking a stable three-dimensional structure. However, the boundary between the two is not well defined and lies near 20–30 residues. Polypeptide can refer to any single linear chain of amino acids regardless of length, but implies an absence of a defined conformation. Proteins can interact with many types of molecules, including with other proteins, with lipids, with carboyhydrates, with DNA, it has been estimated. Smaller bacteria, such as Mycoplasma or spirochetes contain fewer molecules, on the order of 50,000 to 1 million. By contrast, eukaryotic cells are larger and thus contain much more pro
The X chromosome is one of the two sex-determining chromosomes in many organisms, including mammals, is found in both males and females. It is a part of the XY sex-determination X0 sex-determination system; the X chromosome was named for its unique properties by early researchers, which resulted in the naming of its counterpart Y chromosome, for the next letter in the alphabet, following its subsequent discovery. It was first noted. Henking was studying the testicles of Pyrrhocoris and noticed that one chromosome did not take part in meiosis. Chromosomes are so named because of their ability to take up staining. Although the X chromosome could be stained just as well as the others, Henking was unsure whether it was a different class of object and named it X element, which became X chromosome after it was established that it was indeed a chromosome; the idea that the X chromosome was named after its similarity to the letter "X" is mistaken. All chromosomes appear as an amorphous blob under the microscope and only take on a well defined shape during mitosis.
This shape is vaguely X-shaped for all chromosomes. It is coincidental that the Y chromosome, during mitosis, has two short branches which can look merged under the microscope and appear as the descender of a Y-shape, it was first suggested that the X chromosome was involved in sex determination by Clarence Erwin McClung in 1901. After comparing his work on locusts with Henking's and others, McClung noted that only half the sperm received an X chromosome, he called this chromosome an accessory chromosome, insisted that it was a proper chromosome, theorized that it was the male-determining chromosome. Luke Hutchison noticed that a number of possible ancestors on the X chromosome inheritance line at a given ancestral generation follows the Fibonacci sequence. A male individual has an X chromosome, which he received from his mother, a Y chromosome, which he received from his father; the male counts as the "origin" of his own X chromosome, at his parents' generation, his X chromosome came from a single parent.
The male's mother received one X chromosome from her mother, one from her father, so two grandparents contributed to the male descendant's X chromosome. The maternal grandfather received his X chromosome from his mother, the maternal grandmother received X chromosomes from both of her parents, so three great-grandparents contributed to the male descendant's X chromosome. Five great-great-grandparents contributed to the male descendant's X chromosome, etc; the X chromosome in humans spans more than 153 million base pairs. It represents about 800 protein-coding genes compared to the Y chromosome containing about 70 genes, out of 20,000–25,000 total genes in the human genome; each person has one pair of sex chromosomes in each cell. Females have two X chromosomes, whereas males have one Y chromosome. Both males and females retain one of their mother's X chromosomes, females retain their second X chromosome from their father. Since the father retains his X chromosome from his mother, a human female has one X chromosome from her paternal grandmother, one X chromosome from her mother.
This inheritance pattern follows the Fibonacci numbers at a given ancestral depth. Genetic disorders that are due to mutations in genes on the X chromosome are described as X linked. If X chromosome has a genetic disease gene, it always causes illness in male patients, since men have only one X chromosome and therefore only one copy of each gene. Females, may stay healthy and only be carrier of genetic illness, since they have another X chromosome and possibility to have healthy gene copy. For example hemophilia and red-green colorblindness run in family this way; the X chromosome carries hundreds of genes but few, if any, of these have anything to do directly with sex determination. Early in embryonic development in females, one of the two X chromosomes is randomly and permanently inactivated in nearly all somatic cells; this phenomenon is called X-inactivation or Lyonization, creates a Barr body. If X-inactivation in the somatic cell meant a complete de-functionalizing of one of the X-chromosomes, it would ensure that females, like males, had only one functional copy of the X chromosome in each somatic cell.
This was assumed to be the case. However, recent research suggests that the Barr body may be more biologically active than was supposed; the partial inactivation of the X-chromosome is due to repressive heterochromatin that compacts the DNA and prevents the expression of most genes. Heterochromatin compaction is regulated by Polycomb Repressive Complex 2; the following are some of the gene count estimates of human X chromosome. Because researchers use different approaches to genome annotation their predictions of the number